Fix issue with date exclusion

Basically, I'm new to js and just learned typeof doesn't work with dates. I'm pretty sure there's a less atrocious way to check this, but it's what I've got now.

lib/event.js

@@ -353,12 +353,12 @@ var ICalEvent = function(_data, calendar) {
 
             data.repeating.exclude = [];
             repeating.exclude.forEach(function(excludedDate) {
-                if(typeof excludedDate !== 'date') {
+                if(Object.prototype.toString.call(excludedDate) === '[object Date]') {
                     throw '`repeating.exclude` contains invalid value `' + excludedDate + '`!';
                 }
 
                 data.repeating.excludedDate.push(excludedDate);
-            })
+            });
         }
 
         return this;